The present invention relates to a method for driving sheet piles into the ground.
The use of sheet piles for constructing retaining walls is well known. The sheet piles used in such walls have sheet pile interlocks along their longitudinal edges, which can be interlocked so as to maintain the longitudinal edges of adjacent sheet piles interconnected with each other. Current sheet pile interlocks of the double-hook interlock type (type 1 according to EN10248 norm), as e.g. LARSSEN type sheet pile interlocks, are hook shaped elements with an internal interlock chamber. A sheet pile wall is formed by driving a first sheet pile into the ground, introducing the bottom end of the trailing sheet pile interlock of a second sheet pile with the top end of the leading sheet pile interlock of the first sheet pile, driving the second sheet pile into the ground, and then repeating the process to insert third, fourth etc sheet piles into the wall.
It is often necessary to seal the connection between two sheet piles. This is generally done by providing sealing means in at least one interlock chamber of the two interlocking sheet pile interlocks. In order to ensure good sealing conditions, it is important to keep ground material out of the interlock chambers.
Sometimes it is also necessary to interlock two interconnected sheet pile against longitudinal shifting relative to one another. This can be achieved e.g. by bonding the interlocked sheet pile interlocks with an adhesive or cement. In order to ensure good bond conditions, it is important to keep ground material out of the interlock chambers.
Several methods have been proposed for keeping ground material out of the interlock chambers.
EP-0 628 662 teaches to keep the ground material out of the interlock chamber by introducing a steel tube into the interlock chamber of the leading sheet pile interlock or, alternatively, by filling this chamber with a polyethylene tube. In order to be effective, such a tube must closely fit into the interlock chamber. It follows that it is not easy to withdraw the tube from the interlock chamber prior to driving the next sheet pile. This is in particular true, because the leading sheet pile interlock may be slightly deformed when driven into the ground and because ground particles entering between the tube and the wall of the sheet pile interlock increase friction.
According to EP-0 341 194, a caliber piece, which has substantially the same shape as a sheet pile interlock, is interconnected with a leading sheet pile interlock for blocking off the longitudinal opening of the interlock chamber from the outside. Once the sheet pile is driven into the ground, the caliber piece is extracted. Although the interlock chamber is rather well protected from soil, the removal of the caliber piece over the whole length of the sheet pile is not easy.
Similarly, according to GB-2 322 658 a steel conduit is inserted into the interlock chamber. The conduit has a cover attached to it, which blocks off the longitudinal opening of the interlock chamber from the outside. The interlock chamber is rather well protected from soil, but it is very difficult to withdraw the long and rigid conduit-cover assembly from the interlock chamber.
In accordance with EP-0 722 017 the interlock chamber of the leading sheet pile interlock is protected by means of a deformable strip, which is welded with one of its longitudinal edges to the sheet pile, so as to cover the longitudinal opening of the interlock chamber. A major disadvantage of this method is that the deformable strip is easily damaged and torn off when the sheet pile is driven into the ground.
The technical problem underlying the present invention is to provide a method for driving a sheet pile into the ground, wherein the interlock chamber in the sheet pile interlock is well protected from ground material by an obturating device that is easy to introduce and easy to withdraw from the interlock chamber. This problem is solved by a method as claimed in claim 1.
In accordance with the method of the present invention an obturating device comprising an inflatable tube is inserted into the interlock chamber of the sheet pile interlock to be protected. Once the obturating device is in place within the interlock chamber, its inflatable tube is inflated, so that the obturating device effectively closes the opening to the interlock chamber. It follows that no ground material can enter the interlock chamber while the sheet pile is being driven into the ground. Once the sheet pile is in place, the inflatable tube is again deflated, and the obturating device can be easily withdrawn from the interlock chamber. In short, while the inflatable tube is inflated, the obturating device ensures excellent protection for the interlock chamber against ground material, and while the inflatable tube is deflated, the obturating device can be easily inserted into or withdrawn from the interlock chamber.
In accordance with a preferred embodiment, inflation of the inflatable tube pushes an obturating block into the longitudinal opening of the interlock chamber. This obturating block closes the longitudinal opening of the interlock chamber. It will be appreciated that the obturating block can be made stronger than the inflatable tube and is hence less likely to be damaged during the driving process. It is preferably a semi-rigid body, because such a semi-rigid body may be more easily introduced in and withdrawn from the interlock chamber. Furthermore, it is preferably a wedge shaped body engaging the longitudinal opening of the interlock chamber. The wedge shape ensures that, when the inflatable tube is inflated, the obturating block centres itself in the longitudinal opening of the interlock chamber so as to effectively obturate this opening from the inside of the interlock chamber. It is not excluded to conceive the obturating block as a separate piece, but is preferred to firmly attach it to the inflatable tube and, in particular, to form it in one piece with the inflatable tube. The fact that the inflatable tube and obturating block are firmly attached together allows for easy manipulation on the building site.
The obturating device can further comprise a flexible tube with an open front end alongside the inflatable tube which has a closed front end. This flexible tube can then be used for filling the interlock chamber with sand or synthetic foam (as e.g. a PU foam) while the obturating device is withdrawn from the interlock chamber. Especially in case the sheet piles are driven into light or muddy ground material, it is advantageous to fill the interlock chamber with sand or synthetic foam material in order to prevent light or muddy ground material to enter the interlock chamber once the obturating device has been withdrawn. It is not excluded to conceive the flexible tube as a separate piece, but is preferred to firmly attach it to the inflatable tube and, in particular, to form it in one piece with the inflatable tube.
In particular, when constructing a sheet pile wall, the obturating device is inserted into the interlock chamber of the leading sheet pile interlock of a first sheet pile. The inflatable tube is inflated, e.g. by means of compressed air, and this first sheet pile is driven into the ground. Once this first sheet pile is in place, the inflatable tube is deflated and the obturating device is withdrawn from the interlock chamber. It will be appreciated that the withdrawn obturating device leaves an interlock chamber in the leading sheet pile interlock that is perfectly clean, i.e. free from any ground material. The obturating device is then inserted into the interlock chamber of the leading sheet pile interlock of a second sheet pile and the inflatable tube is inflated. The bottom end of the trailing sheet pile interlock of the second sheet pile is now interconnected with the top end of the leading sheet pile interlock of the first sheet pile. As the second sheet pile is driven into the ground, its trailing sheet pile interlock slides down through the clean interlock chamber of the leading sheet pile interlock of the first sheet pile. Once the sheet pile is in place, the inflatable tube is again deflated and the obturating device withdrawn. This process is repeated for the third, fourth, fifth, etc sheet piles. Consequently, the trailing sheet pile interlock of a sheet pile is always interconnected with a clean leading sheet pile interlock of the preceding sheet pile.
Before driving a sheet pile into the ground, it is recommended to insert a front end obturator in the bottom end of the interlock chamber of a leading sheet pile interlock. The front end obturator displaces ground material from under the axial opening of the interlock chamber and prevents ground material from axially entering the interlock chamber. It will be appreciated that the front end obturator can e.g. be a simple bolt. However, in order to be most effective, the front end obturator advantageously has a conical head. The front end obturator is preferably just inserted into the interlock chamber, rather than fixed to the sheet pile, so that the front end obturator can simply be pushed out of the interlock chamber of the leading sheet pile interlock by the trailing sheet pile interlock of the subsequent sheet pile. This is of particular interest in case a sheet pile needs to be driven deeper into the ground than the preceding one.
An adhesive is preferably applied onto the trailing sheet pile interlock of the second sheet pile before interlocking it with the leading sheet pile interlock of the first sheet pile. Thus, the connection joint between two sheet piles is interlocked against longitudinal shifting relative to one another. A spreader can be used for applying the adhesive onto the trailing sheet pile interlock. By using such a spreader, the adhesive is applied onto the trailing sheet pile interlock uniformly over the whole length of the sheet pile.
A sealant can also be applied onto the trailing sheet pile interlock of the second sheet pile before interlocking it with the leading sheet pile interlock of the first sheet pile. Thus, the connection joint between two sheet piles is sealed, and the sheet pile wall can thereby be rendered waterproof. As ground material is kept out of the interlock chambers, excellent sealing conditions between two sheet piles are ensured.
A short cleaning piece is preferably engaged with the leading sheet pile interlock of a first sheet pile before interconnecting this interlock with the trailing sheet pile interlock of a second sheet pile. When the second sheet pile is driven into the ground, its trailing sheet pile interlock pushes the cleaning piece along the leading sheet pile interlock of the first sheet pile. It will be appreciated that the cleaning piece can e.g. be a piece of an interlocking sheet pile interlock, which removes any ground material from the inner walls of the leading sheet pile interlock and preferably wraps the outer walls of the leading sheet pile interlock, so that it also effectively removes any ground material from the outer walls of the leading sheet pile interlock. It follows that all exterior and interior contact surfaces of the leading sheet pile interlock are free of ground material when coming into contact with the corresponding contact surfaces of the trailing sheet pile interlock of the subsequent sheet pile. Usage of the cleaning piece is particularly of advantage if the interlock chamber of the leading sheet pile interlock of the first sheet pile has been filled with sand while the obturating device was withdrawn from the interlock chamber.
The present invention also concerns a device for obturating an interlock chamber of a sheet pile interlock to be used with the method described above. Such an obturating device comprises an inflatable tube arranged in the interlock chamber and a wedge shaped obturating block associated with the inflatable tube.